The present invention relates to an ultraviolet/infrared absorbent low transmittance glass. Particularly, it relates to an ultraviolet/infrared absorbent low transmittance glass which has low visible light transmittance, low solar energy transmittance and low ultraviolet transmittance, and which has a bronze or gray color shade so that it is useful for a window of a vehicle and a building, especially for a privacy protecting glass in a rear window of a vehicle.
Recently, a variety of glasses having ultraviolet and infrared absorptivity to be used as a vehicle windshield has been proposed with the view of preventing color degradation of interior materials and reducing cooling load of the vehicle. Such kinds of glasses include an ultraviolet/infrared absorbent glass having a bronze or gray color shade as the followings.
For example, a window glass of a vehicle disclosed in Japanese Patent Publication No. H5-58670A which is superior in the ultraviolet and infrared absorptivity consists of soda-lime-silica glass including cerium oxide of 0.1 to 1 wt. %, iron oxide expressed as Fe.sub.2 O.sub.3 of 0.2 to 0.6 wt. %, CoO of 0 to 0.005 wt. %, NiO of 0 to 0.01 wt. % and Se of 0.0005 to 0.005 wt. %.
An ultraviolet/infrared absorbent glass having a bronze color shade disclosed in Japanese Patent Publication No. H9-169541A consists of soda-lime-silica glass including total iron oxide expressed as Fe.sub.2 O.sub.3 (T-Fe.sub.2 O.sub.3) of 0.25 to 0.45 wt. %, CeO.sub.2 of 0.8 to 2.0 wt. %, TiO.sub.2 of 0 to 1.0 wt. %, CoO of 0 to 0.005 wt. %, Se of 0.0005 to 0.005 wt. % and FeO expressed as Fe.sub.2 O.sub.3 of 15.5 to 25.0 wt. % of T-Fe.sub.2 O.sub.3.
A privacy protecting glass having low visible light transmittance is often preferred for use particularly in a rear window of a vehicle. Such kinds of glasses are given as the followings.
A neutral dark gray colored glass disclosed in claim 25 of U.S. Pat. No. 5,393,593 consists of soda-lime-silica glass including colorants consisting of 1.00 to 2.2 wt. % Fe.sub.2 O.sub.3 (total iron), at least 0.20 wt. % FeO, 0.0005 to 0.005 wt. % Se, and 0.010 to 0.030 wt. % CoO. The glass exhibits a luminous transmittance of equal to or less than 35% and a total solar infrared transmittance of equal to or less than 20% at a thickness of 3.9 mm.
A dark gray colored glass disclosed in Japanese Patent Publication No. H8-157232A consists of soda-lime-silica glass including colorants consisting of 0.8 to 1.4 wt. % Fe.sub.2 O.sub.3 (total iron), equal to or less than 0.21 wt. % FeO, 0.05 to 1.0 wt. % TiO.sub.2, 0.02 to 0.05 wt. % CoO, and 0.0005 to 0.015 wt. % Se.
A gray colored glass disclosed in Japanese Patent Publication No. H8-67526A consists of soda-lime-silica glass including colorants consisting of 0.15 to 1.2 wt. % Fe.sub.2 O.sub.3 (total iron), equal to or less than 0.30 wt. % FeO, 60 to 180 ppm CoO, 0 to 30 ppm Se, and 0 to 550 ppm NiO. The glass having a thickness of 3.9 mm exhibits the visual appreciation transmittance of 20 to 50%.
A neutral colored soda-lime-silica glass compound disclosed in PCT Application of Japanese Translated Publication No. H7-508971A consists of about 1.3 to about 2 wt. % Fe.sub.2 O.sub.3 (total iron), about 0.01 to about 0.05 wt. % NiO, about 0.02 to about 0.04 wt. % CO.sub.3 O.sub.4, about 0.0002 to about 0.003 wt. % Se wherein a rate of ferrous iron is 18 to 30% and a light and shade coefficient is equal to or less than 0.53.
The window glass of a vehicle disclosed in Japanese Patent Publication No. H5-58670A and the ultraviolet/infrared absorbent glass disclosed in Japanese Patent Publication No. H9-169541A have high transmittance so that the glasses can not be provided with the property of privacy protection equivalent to the present invention. The glasses have a disadvantage of being inferior especially in the infrared absorptivity because of their short content of the total iron.
The neutral dark gray colored glass disclosed in U.S. Pat. No. 5,393,593 contains a large amount of the total iron oxide and is substantially free of nickel. In such glasses containing a large amount of the total iron oxide, the absorption range of the iron ion varies during the reinforcement with air blast cooling, so that the glasses are tinged with yellow. Such discoloration is not preferable for the low transmittance glass having a bronze or gray color shade.
The dark gray colored glass disclosed in Japanese Patent Publication No. H8-157232A which includes TiO.sub.2 as an essential component in the range of 0.05 to 1.0 wt. % is not preferable because TiO.sub.2 is expensive to increase the batch cost and the glass is tinged with yellow to be worsened in the appearance as though it is attached with tar on its surface.
The gray colored glass compound disclosed in Japanese Patent Publication No. H8-67526A is short of the total iron, especially of FeO which contributes to absorption of the heat rays, so that the glass is not preferable because the glass can not be provided with enough heat rays absorptivity under the moderate redox condition. When the amount of the total iron is insufficient, even though it is possible to increase the amount of FeO due to radical reducing fusion, such reducing fusion is not preferable because it may cause obstacles including effusion of streaks with enough silica and silica scum to production in a conventional glass melting furnace.
The neutral colored soda-lime-silica glass compound disclosed in the PCT Application of Japanese Translated Publication No. H7-508971A has a neutral gray color tone, which is precisely a so-called greenish gray color tone having the chromaticity fixed at a*-coordinate of around 4 and b*-coordinate of around 3 on the chromaticity coordinates. The glass has a disadvantage externally in that the interior furnishings are tinged with green and seem to discolor when seen through the glass as compared with a glass having a neutral gray color tone.